21204971 has 4 divisors (see below), whose sum is σ = 21247632. Its totient is φ = 21162312.

The previous prime is 21204949. The next prime is 21205021. The reversal of 21204971 is 17940212.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is not a de Polignac number, because 21204971 - 2²² = 17010667 is a prime.

It is a super-2 number, since 2×21204971² = 899301590221682, which contains 22 as substring.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 21204971.

It is not an unprimeable number, because it can be changed into a prime (21204571) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 20576 + ... + 21581.

It is an arithmetic number, because the mean of its divisors is an integer number (5311908).

Almost surely, 2^21204971 is an apocalyptic number.

21204971 is a deficient number, since it is larger than the sum of its proper divisors (42661).

21204971 is an equidigital number, since it uses as much as digits as its factorization.

21204971 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 42660.

The product of its (nonzero) digits is 1008, while the sum is 26.

The square root of 21204971 is about 4604.8855577528. The cubic root of 21204971 is about 276.7871311343.

The spelling of 21204971 in words is "twenty-one million, two hundred four thousand, nine hundred seventy-one".